In conjunction with solid product release mechanisms, it is often necessary to determine when additional product needs to be released or when enough product has been released. When a storage bin is full, it is desirable to prevent the release of additional products; and conversely, when the storage bin is empty, it is desirable to automatically release more products. However, determining the level of accumulation of solid products, such as ice, is difficult due to the irregular arrangement of the solid products.
For instance, in automatic ice-making machine applications, several known methods have been developed for determining the level of accumulation of ice in a storage bin. One known method of determining the fill level of the storage bin makes use of a sensing arm as disclosed in U.S. Pat. Nos. 5,261,248, issued to Willis et al., 4,635,444, issued to Mawby et al., and 4,680,943, issued to Mawby et al. However, contact sensors will produce inaccurate results if the objects being sensed do not come into contact with the sensor.
Alternatively, non-contact sensors, such as optical interruption or proximity sensors, ultrasonic proximity sensors, capacitive proximity sensors and magnetic proximity sensors can be used to determine the fill level of an ice storage bin. For example, U.S. Pat. No. 4,822,996, issued to Lind discloses the use of a light interrupter system to determine the level of ice in a storage bin. These types of sensors, however, have varied responses due to contamination and changes in material. There is also a significant cost associated with these types of sensors.
For example, a two-element sensor that indicates when a storage bin needs to be refilled, i.e., "bin refill", and when the bin is full, i.e., "bin full", requires a spacing between the two sensors which necessarily depends on the shape and dimensions of the storage bin. The two sensors may be farther apart in a tall storage bin versus a shorter storage bin. In this application, the two sensor configurations are not interchangeable and have to be matched to the particular storage bin used.
A common solution is to pre-configure the sensor for a given type of storage bin. Another solution is to pre-calibrate the sensor of a given type of storage bin and mount that sensor only on that type of storage bin.
Another problem arises in that, even if two storage bins are identical, the release mechanisms and the product released may vary from application to application. With a fast responding release mechanism in a constant usage situation, it might be desirable to have a "bin refill" level set at a comparably low level, thereby decreasing the number of times that the release mechanism is cycled on and off. However, if the release mechanism is slow to respond and usage is heavy but intermittent, the "bin refill" level might be set higher to prevent the storage bin from being emptied before the mechanism can respond. With light usage applications, the "bin refill" level could be set lower to minimize cycling since there would be time to refill the storage bin before the bin is emptied.
To accommodate variations in the "bin refill" level at a user's location, the sensors are configurable at the point of application. In the case of discrete sensors, the separation between the two sensors must be physically changed. Since the sensors are accessible and movable, the sensors are susceptible to shock and vibration.
An alternative to using an array of discrete sensors is to use a single ranging sensor that can operate over a broad range of bin depths. One such sensor type is found in U.S. Pat. No. 5,182,925, issued to Alvarez et al. The level of ice in the storage bin is determined based on the amount of time it takes to receive an echo of a transmitted signal. However, a storage bin equipped with such a sensor still requires the sensor or control system set for the desired "bin refill" and "bin full" values. Additionally, when an indication of the amount of material in the bin is required, it is also desirable to have the system set for "bin empty."
As in sensor arrays, it is possible to have a controller for the release mechanism or a controller for the ultrasonic ranging sensor preset. In such cases, the controller is pre-loaded with the appropriate values for a given storage bin type in a given application for a specific product type with a specific usage rate. However, this forces the sensor and/or release mechanism manufacturer to track and control the assembly, and stock and ship numerous system types. It also limits the end user's flexibility and complicates sensor repair or replacement.